The proposed program is a continuation of the productive effort that has gone into the area of polyene photochemistry, vitamin A and visual pigments for the last decade. It will emphasize exploration of many important leads that have already been established. The projects can be grouped into two major categories. First there will be a continued effort in the investigation of fundamental properties of excited polyenes with an emphasis on understanding of factors governing relaxation processes that channels into specific isomerization reactions. The photochemical knowledge will be combined with the synthetic expertise already established in our laboratory for development of new synthetic methodologies of vitamin A isomers, analogs and carotenoids. A related but more biologically oriented program is the study of fundamental processes and structural properties of visual pigments and their analogs. The information of particular concern is the nature of the photochemical transformation, the shape of the binding site of opsin and detection of specific protein-substrate interactions. There will be a continued collaborative interaction with several biological and spectroscopic research groups. Similar studies with the related bacteriorhodopsin will also be conducted. To achieve these goals we intend to continue our unique approach in combining synthetic skills and physical organic reasoning and methodologies. In addition to the established techniques of photochemical measurements, spectroscopic methods (electronic and nmr) we propose the addition of molecular modelling capability. All these are directed toward a better understanding of the excited state properties of polyenes including the molecular processes in the visual chromophore.